1. Technical Field
The present invention relates to a carbon-coated active material composite, an electrode, and a lithium ion battery, and particularly to a carbon-coated active material composite that is a cathode material for batteries, furthermore, a carbon-coated active material composite preferably available as a cathode material for lithium ion batteries, and a lithium ion battery including a cathode which includes the carbon-coated active material composite.
2. Background
In recent years, as a battery anticipated to have small size, light weight, and high capacity, a non-aqueous electrolytic solution-based secondary battery such as a lithium ion battery has been proposed and put into practical use.
The lithium ion battery is constituted of a cathode and an anode which allow the reversible insertion and removal of lithium ions, and a non-aqueous electrolyte.
Regarding an anode material for lithium ion batteries, as an anode active material, generally, a lithium-containing metal oxide allowing the reversible insertion and removal of lithium ions such as a carbon-based material or lithium titanate (Li4Ti5O12) is used.
On the other hand, regarding a cathode material for lithium ion batteries, as a cathode active material, generally, a lithium-containing metal oxide allowing the reversible insertion and removal of lithium ions such as lithium iron phosphate (LiFePO4) or an electrode material mixture including a binder and the like is used. In addition, the cathode in the lithium ion battery is formed by applying the electrode material mixture to the surface of a metal foil called a current collector.
Compared with secondary batteries of the related art such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries, lithium ion batteries have a lighter weight, a smaller size, and higher energy, and thus are used not only as small-size power supplies in portable electronic devices such as mobile phones and notebook personal computers but also as large-size stationary emergency power supplies.
In addition, recently, studies have been underway regarding the use of lithium ion batteries as high-output power supplies for plug-in hybrid vehicles, hybrid vehicles, and electric power tools, and batteries used as the high-output power supplies are required to have high-speed charge and discharge characteristics.
However, electrode active materials, for example, electrode materials including a lithium phosphate compound allowing the reversible insertion and removal of lithium ions have a problem of low electron conductivity. Therefore, to increase the electron conductivity of electrode materials, there has been proposed an electrode material in which the particle surfaces of an electrode active material are covered with an organic compound that is a carbon source, and then the organic compound is carbonized, whereby a carbonaceous film is formed on the surface of the electrode active material, and carbon in the carbonaceous film is interposed as an electron conductive substance (For example, Japanese Laid-open Patent Publication No. 2001-15111).